1. Field of the Invention
The present invention relates to a field-effect transistor (hereinafter, referred to as an xe2x80x9cFETxe2x80x9d) used in a microwave band. In particular, the present invention relates to a GaAs power FET element having an internal matching circuit.
2. Description of the Related Art
There is an increasing demand for a GaAs FET as a device for mobile communication equipment such as a mobile phone, due to its excellent high-frequency characteristics. Particularly, a GaAs power FET is applied, as an amplifier of power for transmission, to a base station as well as a terminal of a mobile phone, and such an FET contributes to the miniaturization and low power consumption of the base station due to its high-output and high-efficiency characteristics. In the present specification, various high-frequency devices such as a power FET, a low-noise FET, and a mixer will be referred to collectively as a high-frequency semiconductor device.
Hereinafter, a conventional high-frequency semiconductor device will be described.
FIGS. 12A and 12B are schematic views of a conventional GaAs power FET element having an internal matching circuit. FIG. 12A is a plan view showing the inside of the FET element, and FIG. 12B is across-sectional view taken along a line Exe2x80x94Exe2x80x2 in FIG. 12A
In FIGS. 12A and 12B, a package 17 has a configuration in which a frame 16 made of ceramic is welded to a bottom portion 13 mainly made of copper. The bottom portion 13 is plated with gold. FET chips 1a and 1b are mounted substantially at a central portion of the package 17. An incoming dielectric substrate 91 made of ceramic is mounted on an input side of the FET chips 1a and 1b. An incoming distributed constant line 93 is formed on the surface of the incoming dielectric substrate 91. An outgoing dielectric substrate 92 is mounted on an output side of the FET chips 1a and 1b. An outgoing distributed constant line 94 is formed on the surface of the outgoing dielectric substrate 92. An input terminal 10 and the incoming distributed constant line 93 are connected electrically to each other via bonding wires 19. Similarly, the incoming distributed constant line 93 and the FET chips 1a, 1b; the FET chips 1a, 1b and the outgoing distributed constant line 94; and the outgoing distributed constant line 94 and an output terminal 12 respectively are connected to each other via the bonding wires 19.
In order to obtain a high-frequency power from the power FET, it is required to form an input impedance matching circuit and an output impedance matching circuit outside of the power FET so as to reduce the reflection of a high-frequency power.
Since the total gate width of the FET chips 1a and 1b is very large, the input and output impedances thereof are very low (i.e., 1 xcexa9 or less). Thus, when it is attempted to obtain an impedance matching circuit directly in such a low impedance state, optimum matching conditions are not obtained, and a power loss becomes very large. In order to obtain power from the FET efficiently, it is important that the impedance of the FET is once converted to a high level (about 10 xcexa9). In general, the incoming distributed constant line 93 and the outgoing distributed constant line 94 also are called internal matching circuits and designed so as to realize such impedance conversion.
An abnormal oscillation, which can be a serious problem in using the power FET element, will be described below.
In the FET elements in FIGS. 12A and 12B, the case where there is a variation in a threshold value (Vth) and a mutual conductance (gm) between regions M and N of the FET chip 1a will be considered. For example, in the case where a high-frequency power output from the region M of the FET chip 1a is larger than that output from the region N, a roundabout power 96 is generated on the outgoing distributed constant line 94. The roundabout power 96 becomes a reflection power to the region N, whereby the impedance on the output side seen from the region N is changed. More specifically, a difference in impedance on the output side is caused between the regions M and N. As a result, a power imbalance further is increased, resulting in an abnormal oscillation. According the actual measurement, when there is a difference of 0.2 V in a threshold voltage between the regions M and N, an abnormal oscillation was caused in the vicinity of the maximum output.
Next, the case where there is a variation in Vth and gm between the FET chips 1a and 1b will be considered. For example, in the case where a high-frequency power output from the FET chip 1a is larger than that output from the FET chip 1b, a roundabout power 97 is generated on the outgoing distributed constant line 94. When the roundabout power 97 is generated, a reflection power to the FET chip 1b is increased, resulting in a change in impedance on the output side seen from the FET chip 1b. More specifically, a difference in impedance on the output side is caused between the FET chips 1a and 1b, and the difference in high-frequency power to be output further is increased. A power imbalance is increased, resulting in an abnormal oscillation.
The abnormal oscillation is caused not only when the FET chips 1a and 1b are varied, but also when an imbalance is likely to be caused in an operation of the FET chips 1a and 1b (e.g., under a transient condition (during power-on) or when an unnecessary signal is input instantaneously). When an abnormal oscillation is caused, an interference wave not only has an adverse effect on radio communication, but also damages the FET element, which is a serious problem in terms of reliability.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a high-frequency GaAs power FET element with high performance, capable of suppressing an abnormal oscillation.
In order to achieve the above-mentioned object, a first high-frequency semiconductor device of the present invention includes: an amplifier; a dielectric substrate provided on an input side or an output side of the amplifier; a plurality of transmission lines formed on a surface of the dielectric substrate and connected electrically to the amplifier; and a resistor formed on the surface of the dielectric substrate and connected electrically between the plurality of transmission lines.
In the first high-frequency semiconductor device, it is preferable that the plurality of transmission lines have an electrical length of substantially xcex/4 with respect to an operation frequency, and the resistor has the same length as that of the plurality of transmission lines in a traveling direction of a high-frequency power.
In order to achieve the above-mentioned object, a second high-frequency semiconductor device of the present invention includes: first and second amplifiers; a dielectric substrate provided on an input side or an output side of the first and second amplifiers; a first transmission line formed on a surface of the dielectric substrate and connected electrically to the first amplifier; a second transmission line formed on a surface of the dielectric substrate and connected electrically to the second amplifier; and a resistor formed on a surface of the dielectric substrate and connected electrically between the first and second transmission lines.
In the second high-frequency semiconductor device, it is preferable that the first and second transmission lines have an electrical length of substantially xcex/4 with respect to an operation frequency, and the resistor has the same length as those of the first and second transmission lines in a traveling direction of a high-frequency power.
In order to achieve the above-mentioned object, a third high-frequency semiconductor device includes: first and second amplifiers; a dielectric substrate provided on an input side or an output side of the first and second amplifiers; a first transmission line formed on a surface of the dielectric substrate and connected electrically to the first amplifier; a second transmission line formed on a surface of the dielectric substrate and connected electrically to the second amplifier; and a resistor and a third transmission line formed on a surface of the dielectric substrate and connected electrically between the first and second transmission lines.
In the third high-frequency semiconductor device, it is preferable that the first to third transmission lines have an electrical length of substantially xcex/4 with respect to an operation frequency, and the resistor has the same length as those of the first to third transmission lines in a traveling direction of a high-frequency power.
Furthermore, in the third high-frequency semiconductor device, it is preferable that a first resistor, the third transmission line, and a second resistor are connected successively between the first and second transmission lines.
Furthermore, in the third high-frequency semiconductor device, it is preferable that a width of third transmission line is made larger on the first and second amplifier side and smaller on the other side.
In order to achieve the above-mentioned object, a fourth high-frequency semiconductor device of the present invention includes: first and second amplifiers; a dielectric substrate provided on an input side or an output side of the first and second amplifiers; first and second transmission lines formed on a surface of the dielectric substrate and connected electrically to the first amplifier; third and fourth transmission lines formed on a surface of the dielectric substrate and connected electrically to the second amplifier; a first resistor connected between the first and second transmission lines; a second resistor connected between the second and third transmission lines; and a third resistor connected between the third and fourth transmission lines.
In order to achieve the above-mentioned object, a fifth high-frequency semiconductor device of the present invention includes: first and second amplifiers; a dielectric substrate provided on an input side or an output side of the first and second amplifiers; first and second transmission lines formed on a surface of the dielectric substrate and connected electrically to the first amplifier; third and fourth transmission lines formed on a surface of the dielectric substrate and connected electrically to the second amplifier; a first resistor connected between the first and second transmission lines; a second resistor and a fifth transmission line connected between the second and third transmission lines; and a third resistor connected between the third and fourth transmission lines.
In order to achieve the above-mentioned object, a sixth high-frequency semiconductor device of the present invention includes: first and second amplifiers; a dielectric substrate provided on an input side or an output side of the first and second amplifiers; first and second transmission lines formed on a surface of the dielectric substrate and connected electrically to the first amplifier; third and fourth transmission lines formed on a surface of the dielectric substrate and connected electrically to the second amplifier; a first resistor connected between the first and second transmission lines; a second resistor connected between the third and fourth transmission lines; a third resistor connected to an end of the second transmission line opposed to the third transmission line; a fourth resistor connected to an end of the third transmission line opposed to the second transmission line; and a unit for connecting the third and fourth resistors electrically.
In the fourth, fifth, and sixth high-frequency semiconductor devices, it is preferable that the transmission lines have an electrical length of substantially xcex/4 with respect to an operation frequency, and the resistors have the same length as those of the transmission lines in a traveling direction of a high-frequency power.
In order to achieve the above-mentioned object, a seventh high-frequency semiconductor device of the present invention includes: first and second amplifiers; a dielectric substrate provided on an output side or an input side of the first and second amplifiers; first and second transmission lines formed on a surface of the dielectric substrate and connected electrically to the first amplifier; third and fourth transmission lines formed on a surface of the dielectric substrate and connected electrically to the second amplifier; a first resistor connected between the first and second transmission lines; a second resistor connected between the third and fourth transmission lines; a first input terminal or output terminal on a power combining circuit connected electrically to a side of the first and second transmission lines opposite to a side thereof connected to the first amplifier; a second input terminal or output terminal on the power combining circuit connected electrically to a side of the third and fourth transmission lines opposite to a side thereof connected to the second amplifier; and a third resistor connected between the first input terminal and the second input terminal or between the first output terminal and the second output terminal.
In order to achieve the above-mentioned object, an eighth high-frequency semiconductor device of the present invention includes: first and second amplifiers; a dielectric substrate provided on an output side or an input side of the first and second amplifiers; first and second transmission lines formed on a surface of the dielectric substrate and connected electrically to the first amplifier; third and fourth transmission lines formed on a surface of the dielectric substrate and connected electrically to the second amplifier; a first resistor connected between the first and second transmission lines; a second resistor and a fifth transmission line connected between the second and third transmission lines; a third resistor connected between the third and fourth transmission lines; a first input terminal or output terminal on a power combining circuit connected electrically to a side of the first and second transmission lines opposite to a side thereof connected to the first amplifier; and a second input terminal or output terminal on the power combining circuit connected electrically to a side of the third and fourth transmission lines opposite to a side thereof connected to the second amplifier.
In the first, second, and third high-frequency semiconductor devices, it is preferable that widths of the transmission lines are made larger on the amplifier side and smaller on the other side.
In order to achieve the above-mentioned object, a ninth high-frequency semiconductor device of the present invention includes: an amplifier; an incoming dielectric substrate provided on an input side of the amplifier; an outgoing dielectric substrate provided on an output side of the amplifier; an incoming transmission line formed on a surface of the incoming dielectric substrate and connected electrically to the amplifier; and an outgoing transmission line formed on a surface of the outgoing dielectric substrate and connected electrically to the amplifier, wherein a thickness of the incoming dielectric substrate is different from that of the outgoing dielectric substrate.
In the ninth high-frequency semiconductor device, it is preferable that either the incoming transmission line or the outgoing transmission line is provided as a plurality in number, and a resistor is connected between the plurality of transmission lines.
Furthermore, in the ninth high-frequency semiconductor device, it is preferable that a width of the incoming transmission line is equal to that of the outgoing transmission line.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.